The present invention relates in general to furnace dampers, and more specifically, to furnace dampers which can selectively provide fresh air to a furnace while the furnace is in operation, and which can be effectively sealed when the furnace is not in operation.
Newer technologies in home construction have resulted in homes which are more and more "air tight." As a result, these homes are more completely closed and do not allow fresh air to flow into the structure. However, research has shown that a certain amount of fresh air flow is needed to dilute man-made household pollutants which may exist in a home, such as formaldehyde found in paints, volatile organic compounds found in sealants, and toluene found in binders. In order to combat these pollutants, efforts have been made in the area of furnace filter designs to improve the quality of indoor air. However, due to maintenance problems and certain design limitations, these furnace filters do not adequately remove harmful pollutants.
In general, when fresh air flow is increased, the indoor air quality is also increased. At least in part due to these concerns regarding the introduction of fresh air into modern homes, changes were made in the 1991 Uniform Mechanical Code (UMC) provisions regarding fresh air introduction for furnaces with respect to air supply. The UMC now requires that a fresh air intake of 15 cubic feet per minute (cfm) per person be supplied by an outside source. Section 706 of the UMC states:
Circulating air shall be taken from outside the building or from the conditioned space, or both. Heating systems regulated by this code and designed to replace required ventilation shall be arranged to discharge into the conditioned space not less than the amount of outside air specified in the Building Code.
A typical ventilation standard which is used by many engineers is the American Society of Heating, Refrigeration, and Air-Conditioning Engineers Standard 62-1989. This standard recommends 0.35 air changes per hour, but not less than 15 cfm per person fresh air flow.
Attempts have been made to meet this standard by providing a "passive" fresh air system. This passive fresh air system utilizes an air duct that connects an outside air source to the return air duct of the furnace system via a fresh air supply duct. In this passive fresh air system, fresh air is drawn into the return air duct simply from the suction generated by the main blower fan of the furnace. Thus, these passive systems have been designed to rely upon the main blower fan of the furnace to provide the required amount of suction so that a minimum of 15 cfm per person of fresh air is drawn into the return air duct of the furnace system. This passive system does not regulate the amount of fresh air actually entering the system and does not ensure that the standard of 15 cfm per person of fresh air is being met.
Along with the above disadvantages, the passive fresh air systems being used do not prevent fresh air from flowing into the return air duct of the furnace when the main blower fan of the furnace is not operating. Thus, unwanted outside air can enter the return air duct of the furnace system even when the main blower fan of the furnace is not in operation. Unwanted cold air increases the amount of heating the furnace must accomplish, which in turn increases the overall energy costs to the consumer. Further, the entrance of cold air into the return air duct in extremely cold environments can result in damage to pipes which may exist in and around the furnace.
Additional problems also exist when excess cold air enters the return air duct of the furnace system. The cold air may cause the products of combustion (principally carbon monoxide, carbon dioxide and water vapor) to condense on the inner surface of the heat exchanger. This condition creates an environment in which the combustion gasses begin to condense out and cause the formation of carbonic acid. This carbonic acid may damage the interior of the furnace through corrosion, causing a reduction in the useful life of the furnace. If a sufficient amount of corrosion takes place, a health hazard may exist if cracks form in the heat exchanger. The existence of cracks in the heat exchanger can cause the heating chamber to fracture which may allow carbon monoxide to mix with the heated air in the room, or to be exhausted improperly. As is well known, carbon monoxide poisoning can lead to illness and sometimes death.
Therefore, an electrically controlled damper is needed which can inject the proper volume of fresh air into the return air duct of a furnace system. Further, an electrically controlled damper is needed which will substantially prevent unwanted fresh air from entering the return air duct when the furnace is not in operation.